Commercial poly(vinyl acetate) (PVAc) paint formulations for artists include a number of compounds in addition to the PVAc polymer and pigments to improve the physical and chemical properties of the resulting product. Among the most common additives are surfactants, coalescing agents, defoamers, freeze-thaw agents and thickeners. These products significantly influence the behaviour of the dried film. Nevertheless, they are usually difficult to detect with conventional analytical methods given their low concentration. In order to identify these additives, present in the dried film as minor components, an analytical method based on in situ thermally assisted pyrolysis-silylation gas chromatography-mass spectrometry (GC-MS) using hexamethyldisilazane as a derivatisation reagent is proposed. This method improves the conventional GC-MS analysis performed by direct pyrolysis and enables the simultaneous identification of the PVAc binding medium and the additives included by the manufacturer in the commercial paint. Five different commercial PVAc paints have been analysed, namely, armour green, burnt umber, oriental red, raw umber and white from Flashe. Internal plasticiser VeoVa consisting of C(10) fatty acids with highly branched chains has been recognised from the MS spectra. On the other hand, the differences found in the additive content of the studied paints, in particular the poly(ethylene glycol)-type surfactant, are in good agreement with their mechanical properties.

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Evaluation of a gelatin-based adhesive for historic paintings that incorporates citronella oil as an eco-friendly biocide The presented study focuses on evaluating the efficiency of a gelatin-based product that incorporates a plasticizer (glycerol) and a biocide (citronella oil), proposed as an eco-friendly adhesive for polychrome decoration applied in different parts of the architectural complex of the Longshan Temple in Lukang (18th century, Taiwan). Seven laboratory physico-chemical tests were performed: a) viscosity measurement; b) drying curves; c) moisture content determination; d) water vapor permeability test; e) mechanical test; f) adhesion test; g) susceptibility to fungi colonization test, which provide information on the workability, water content and water barrier properties, as well as mechanical, adhesion, and the biocide properties of the proposed product. The obtained results indicate that the workability, mechanical and adhesive properties of the new adhesive are adequate. Permeability in polychromies is slightly reduced due to the additional barrier effect of the adhesive incorporated into the paint film. The efficiency of citronella oil for preventing the growth of fungus Aspergillus niger on paintings consolidated with the adhesive was also probed. In parallel to these laboratory trials, the micro-invasive tests carried out, using nanoindentation combined with atomic force microscopy (NI-AFM), provided direct evidence for the improvement in the mechanical properties induced by applying the new adhesive to the original polychromies.

L’article analyse de manière critique les techniques de facing et la description d’un système novateur fondé sur l’usage de supports temporaires réhumidifiable qui vont permettre d’obtenir une protection superficielle avec une force de liaison appropriée et facilement réversible. Cet article comprend aussi la description de la première partie expérimentale de l’enquête, focalisée sur l’évaluation des caractéristiques des différentes catégories de matériaux (adhésifs et supports temporaires) et leur combinaison pour la réalisation de supports temporaires réhumidifiable.

Influence of the plasticizer and biocide on functional properties of gelatin-based adhesives used in the consolidation of paintings The study presented here focus on the influence of glycerol and citronella oil, added to gelatin dispersions as plasticizer and biocide, respectively, on the mechanical, water barrier and other functional properties of gelatin-based adhesives used in treatments of painting consolidation. For this purpose, ATR-FTIR spectroscopy, gas chromatography-mass spectrometry (GC-MS), atomic force microscopy (AFM) analyses combined with tensile, water vapour permeability, water content and water solubility tests, have been performed on gelatin films prepared by adding glycerol and citronella oil. These two products have been chosen owing to their low toxicity and eco-friendly properties. Evaluation of the modification in the behaviour of the gelatin-based adhesives as consequence of the addition of glycerol and citronella oil has been carried out on the basis of the changes in microstructure of the adhesive and the changes in the three-dimensional structure of the protein molecules due to their interaction with glycerol and the citronella oil, all these data provided by the analytical techniques applied. In a second step, stability to the light of the proposed adhesive has been assessed in order to establish its suitability for painting consolidation. The results obtained suggest that citronella oil enhances the effectiveness of glycerol in improving mechanical and water barrier properties. Light ageing of specimens containing the proposed additives resulted in no remarkable changes in structure, mechanical, water barrier and other functional properties of the adhesives.